1. Field of the Invention
The present invention relates to a strengthened door, and more particularly to a strengthened door for the cargo container need to resist explosive blast.
2. Description of Related Art
A cargo container must have a door pivotally mounted on it to selectively close the cargo container for loading and unloading goods. However, the conventional door for a cargo container does not have a strengthened design or device to resist an explosive blast.
Over a decade, airplanes have become a primary target for terrorist attack, and many people have lost their lives in plane crashes due to terrorist bombs attached in checked baggage. To prevent those tragedies from happening, a lot of efforts have been made in the field of blast-resistant containers.
According to analysis and experiments, the blast-resistant cargo container need to take the blast pressure tens of times greater than the payload of the conventional cargo container. It means that all the surrounding four edges of the door panel must take very great tensile forces under such great explosive pressure in the container. Therefore, the requirements of the door of a blast-resistant cargo container are not only that the door is moveable to be opened and closed for receiving foods as usual, but also that all the four edges of the door panel must be strongly connected to its adjacent container panels under a blast. Hence, the door of conventional cargo container without strengthened design is very vulnerable to the explosive blast.
Many blast-resistant cargo containers have been granted patents by the USPTO, such as U.S. Pat. No. 5,599,082, 6,019,237, and 6,237,793. U.S. Pat. No. 5,599,082 is a hardened aircraft unit load device, which door has a pair of opposed crooked fingers or a T-shaped flange attached along part of the edge of the door to establish a bite for strongly connecting the door panel and its adjacent panels. But the “bite” or interlock mechanism can only be applied to a part of the surroundings of the door. Although another mechanism of “abutment of two contact plates” is offered to compensate, it is not reliable in reality. Hence, there are only a part of the edges (not all four edges) of the door panel can be really strongly connected. It is prone to failure at the non-strongly connected edge when explosion occurs.
U.S. Pat. No. 6,019,237 is a modified container using an inner bag to resist the blast. The bag member includes multiple overlapping door frame folds to reduce the force between the door and the bag opening frame. However, the unreliable mechanism may result in that the length of the connector between the door and the opening frame is too short to resist explosive blast.
U.S. Pat. No. 6,237,793 discloses an explosion resistant aircraft cargo container having a door with two side edges and a bottom edge that can securely connect to its adjacent panels. But the door panel is flexible, i.e., the container door has a curtain design. When opened, the door panel has to be folded several times to complete the operation. Obviously, some damages may occur inside the door panel along the folds after some time of operation. It is a very serious situation for the blast-resistant cargo container because the crews couldn't see the damages to the panel from the outside when interior damages have occurred.
The present invention has arisen to mitigate and/or obviate the disadvantages of the cargo container door, no matter the conventional or blast-resistant cargo container just mentioned above.